S3 DownloadFilter

S3 DownloadFilter 是 Amazon S3 SDK for Java 中的一个过滤器，用于在下载 S3 对象时对其进行修改、过滤或加工。

以下是一个示例代码，可以作为 S3 DownloadFilter 的实现：

import com.amazonaws.services.s3.AmazonS3;
import com.amazonaws.services.s3.model.*;
import com.amazonaws.services.s3.model.S3Object;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

public class MyS3DownloadFilter implements S3DownloadFileFilter {

    private final AmazonS3 amazonS3;

    public MyS3DownloadFilter(AmazonS3 amazonS3) {
        this.amazonS3 = amazonS3;
    }

    @Override
    public S3Object downloadObject(S3Object object, S3ObjectInputStream inputStream, ObjectMetadata metadata) throws IOException {
        // do some modification or processing on the object or its content
        // for example, we can read the object content and replace all "foo" with "bar"
        String content = new String(inputStream.readAllBytes());
        String newContent = content.replaceAll("foo", "bar");
        InputStream newInputStream = new ByteArrayInputStream(newContent.getBytes());
        
        // create a new ObjectMetadata with the updated content length
        ObjectMetadata newMetadata = new ObjectMetadata();
        newMetadata.setContentLength(newContent.length());
        
        // create a new S3Object with the updated content and metadata
        S3Object newObject = new S3Object();
        newObject.setBucketName(object.getBucketName());
        newObject.setKey(object.getKey());
        newObject.setObjectContent(newInputStream);
        newObject.setObjectMetadata(newMetadata);
        
        return newObject;
    }

    @Override
    public void downloadFile(S3Object object, S3ObjectInputStream inputStream, ObjectMetadata metadata, OutputStream outputStream) throws IOException {
        // do some modification or processing on the object or its content
        // for example, we can read the object content and replace all "foo" with "bar"
        String content = new String(inputStream.readAllBytes());
        String newContent = content.replaceAll("foo", "bar");
        InputStream newInputStream = new ByteArrayInputStream(newContent.getBytes());

        // write the updated content to the output stream
        byte[] buffer = new byte[1024];
        int bytesRead;
        while ((bytesRead = newInputStream.read(buffer)) != -1) {
            outputStream.write(buffer, 0, bytesRead);
        }
    }

    @Override
    public boolean equals(Object obj) {
        return obj instanceof MyS3DownloadFilter;
    }

    @Override
    public int hashCode() {
        return 0;
    }
}

这个实现中，我们通过 S3DownloadFileFilter 接口提供的 downloadObject 和 downloadFile 方法，实现了对下载的 S3 对象进行修改和加工的逻辑。在这个例子中，我们读取对象的内容，将所有的 "foo" 替换成 "bar"，然后返回一个新的 S3Object 对象或将修改后的内容写入输出流中。需要注意的是，我们还需要创建一个新的 ObjectMetadata 对象，其中包括更新后的内容长度。